1. Field of the Invention
The present invention relates to a cable drag chain for protecting and guiding safely and surely such flexible members as cable and hose which feed energy to a movable machine. More particularly, this invention relates to an improvement in a link member of the cable drag chain which is composed of a pair of left and right side plates and upper and lower connecting plates connecting upper and lower edges, respectively, of the side plates.
2. Description of the Related Art
Cable drag chains include a plurality of link members connected end to end in a bendable manner. The cable drag chain is connected at one end to a movable machine and at the other end to a fixed frame or a floor surface. Each of the link members has a hollow internal space so that a flexible member such as cable or hose is received in the interior of a continuous hollow internal spaces of the consecutive link members.
One example of such cable drag chains is disclosed in Japanese Utility Model Publication No. HEI-03-52774. In the disclosed cable drag chain, each link member includes a pair of opposed left and right side plates, a lower connecting plate connecting lower edges of the left and right side plates, and an upper connecting plate connecting upper edges of the left and right side plates. The upper connecting plate is hinged to the side plates so that a flexible member can be received in the cable drag chain.
Each of the side plates has an engagement pin provided at a central portion of the upper edge thereof, and the upper connecting plate has a pair of hooks formed at opposite end thereof and adapted to be snap-fit with the respective engagement pins of the side plates. For attaching the upper connecting plate to the side plates, the hook at one end of the upper connecting plates is snap-fit with the engagement pin of one side plate and, subsequently, the upper connecting plate is turned about one end hooked on the engagement pin such that the hook at the opposite end of the upper connecting plate is brought into snap-fitting engagement with the engagement pin of the other side plate.
Another cable drag chain having a different structure is disclosed in Japanese Patent Laid-open Publication No. HEI10-28310 In the disclosed cable drag chain, each link member is comprised of a pair of opposed left and right side plates and upper and lower connecting plates connecting upper and lower edges, respectively, of the side plates. The upper connecting plate is formed integrally with one of the side plates and connected to the one side plate via a hinge portion.
The hinge portion takes the form of recessed portion formed at a junction between the one side plate and the upper connecting plate. For assembling the link member, the upper connecting plate is bent or folded about the recessed hinge portion through an angle of about 90 degrees and, subsequently, a hook formed at a distal end of the upper connecting plate is hooked on the other side plate.
The cable drag chain shown in Japanese Utility Model Publication No. HEI-03-52774 has various problems due to the upper connecting plate formed separately from the side plates, as enumerated below.
(1) The upper connecting plate which is snap-fit at opposite ends with the left and right side plates is likely to be detached from the side plates when the cable drag chain is twisted or otherwise deformed, thus failing to achieve an essential function to receive and protect a flexible member such as cable or hose.
(2) Due to the snap-fit engagement between the opposite ends of the upper connecting plate and the left and right side plates, when one end of the upper connecting plate is detached from one side plate for the maintenance or inspection of the flexible member, the other end of the upper connecting plate is apt to disengage from the other side plate. This may result in a missing upper connecting plate.
(3) The snap-fit engagement between the opposite ends of the upper plate and the left and right side plates gives rise to another problem in that when one end of the upper connecting plate is detached from one side plate for the maintenance or inspection of the flexible member, the upper connecting plate is allowed to turn downward about the other end being snap-fit with the other side plate, thereby hindering smooth and efficient maintenance or inspection of the flexible member.
(4) The upper connecting plate is a separate part and hence requires a special mold for producing the same in addition to a mold used for forming left and right side plates and a lower connecting plate into a unitary structure. Furthermore, a dimensional adjustment work due for achieving dimensional adjustment between the two molds adds to the cost of molds, leading to an excessively high manufacturing cost of the cable drag chain.
(5) Since the upper connecting plate is designed to be snap-fit at opposite ends with the left and right side plates to assemble a single link member, assembly of the overall cable drag chain composed of a number of such link members is laborious and time-consuming,
In addition, in the cable drag chain shown in Japanese Utility Model Publication No. HEI-03-52774, the connecting plate is turned about the engagement pin of one side plate in a direction to cause the hook at the other end of the connecting plate to be snap-fit with the engagement pin of the other side plate. To this end, the hook of the upper connecting plate has a downwardly facing opening for enabling resilient deformation (consecutive radial expansion and contraction) of the hook to grip the engagement pin on the other side plate. This arrangement also causes additional problems as enumerated below.
(6) Since the upper connecting plate and the left and right side plates are connected together by the resiliency of the hooks acting on the engagement pins, the hooks are likely to be detached from the mating engagement pins when subjected to an external force or the weight of the flexible member. When such detachment occurs, the cable drag chain is no longer able to perform the prescribed receiving and protecting function with respect to the flexible member such as cable or hose.
(7) Since the opening of the hook is oriented in a direction tangent to the other end of the connecting plate, an attempt to narrow the hook opening to deal with the problem described at the preceding paragraph (6) would result in a great muscular effort required when the opposite ends of the connecting plates are engaged with the side plates. This lowers the assembling efficiency of the cable drag chain.
On the other hand, the cable drag chain shown in Japanese Patent Laid-open Publication No. HEI-10-28310 has an upper connecting plate formed integrally with one side plate and, hence, is free from a problem of missing upper connecting plate and can be manufacturing at a relatively low cost as compared to the cable drag chain shown in Japanese Utility Model Publication No. HEI-03-52774. However, the cable drag chain, due to a low rigidity of the hinge portion and a body thereof, still has problems, as enumerated below.
(1) Since the body of the cable drag chain is made so thin as to have a desired degree of bendability, and since the hinge portion is made excessively thin and hence is low in rigidity for enabling easy opening and closing of the upper connecting plate relative to the side plates, the hook at the distal end of the upper connecting plate is likely to be disengaged from the other side plate when the upper connecting plate is subjected to the weight of the flexible member, thus allowing the flexible member to project outward from the hollow internal space of the cable drag chain.
(2) In the case where the flexible member received in the cable drag chain is composed of plural flexible elements of different weights, an unbalanced load occurs. When subjected to such unbalanced load, the cable drag chain body comprised of a continuous elastic member is liable to be twisted due to insufficient rigidity. When the cable drag chain is rolled, a twist-induced force and a force or weight of the flexible member tending to tilt the side plates sideways are added together, and by thus combined forces, the connection between the upper connecting plate and one of the side plates is likely to be disengaged.
(3) In the case where plural flexible elements are stacked one above another within the hollow internal space of the cable drag chain, an upper part of the stacked flexible elements tends to force the side plates in a lateral outward direction, thereby separating the connection between the upper connecting plate and one of the side plates.
(4) When the cable drag chain is bent during use, a bent portion is subjected to a great load or force due to stoppers of the adjacent link members being held in abutment with each other. In this instance, the left and right side plates are forced to tilt outward away from each other with the result that the hook on the distal end of the upper connecting plate which is directed outward in a horizontal direction is easily disengaged from the side plate.
(5) If the rigidity of the hinge portion is excessively high, the upper connecting plate after being hooked on the side plate is forced to bend arcuately by the resiliency of the hinge portion. When the arcuately bent upper connecting portion is placed on the floor surface to support a body of the cable drag chain during use of the cable drag chain, the cable drag chain becomes unstable in position and is likely to roll down over the floor surface. On the other hand, if the bending strength of the hinge portion is made weak, the rigidity of the cable drag chain body is decreased with the result that the adjustment of the hinge strength is difficult to achieve.
(6) If the engagement strength of the hook is increased, the side plates and the upper connecting plate are susceptible to deformation or yielding due to their low rigidities. This makes-it difficult to engage the hook with a mating portion of the side plate.
(7) When the cable drag chain is in a stretched condition, slits between adjacent link members are closed. Accordingly, there is no room or space provided for allowing free access of a tool such as screwdriver to a joint portion between the upper connecting plate and the side plate when the joint is to be disengaged. In addition, the link members have no portion ready to be grasped. Thus, a joint releasing work is very difficult to achieve.